1. Field of the Invention
The present invention relates to an illumination device including a lens sheet with excellent moldability that can reduce color unevenness without impairing luminance of illumination light.
2. Description of the Related Art
In the past, an incandescent lamp or a fluorescent lamp has been commonly used as a light source for general illumination such as indoor illumination. However, as the performance of today's blue light emitting diode (LED) becomes more advanced, an LED is also used in a light source such as a ceiling light or a downlight (see, for example, JP 2007-220465 A).
FIG. 11 illustrates a so-called pseudo white LED 100, which can be used as a light source of an illumination device. The pseudo white LED 100 includes a lamp house 104, in which a plurality of blue LEDs 102 as light emitting elements is disposed adjacent to one another on a bottom portion thereof, and a transparent resin 106 that seals a concave portion of the lamp house 104. Yellow phosphors 108 such as garnet (YAG) are dispersed in the transparent resin 106. Blue light emitted from the respective blue LEDs 102 is diffused in the transparent resin 106 disposed in the lamp house 104. At this time, the blue light is emitted to the exterior of the lamp house 104 in a state of being wavelength-converted into fluorescent yellow light by the yellow phosphors 108, for convenience, as outgoing light L (L1 and L2) as indicated by a chain double-dashed line. A portion 103 of FIG. 11 is an electrode terminal.
Also, as illustrated in FIG. 12, the outgoing light L from the pseudo white LED 100 is deflected in desired directions by passing through a lens sheet 110 disposed in front of the pseudo white LED 100, which enables a function as the illumination device. In the lens sheet 110 of FIG. 12, a first lens group 112 is disposed on an inner side, when seen from an optical axis C of the pseudo white LED 100 as a reference location, and the first lens group 112 includes refraction prisms. Also, a second lens group 114 is disposed on an outer side of the first lens group 112, and includes reflection (TIR: Total Internal Reflection) prism lenses.
An output angle of the outgoing light L from the pseudo white LED 100 is deflected by both the first lens group 112 and the second lens group 114 to a direction parallel to the optical axis C.
Herein, a case where the lens sheet 110 used in the illumination device described above is formed by an injection molding method will be considered. Generally, in the injection molding method, the lens sheet 110 is formed by injecting a molding material into a molding cavity of a molding die of the lens sheet 110 from a gate G (see FIG. 1B) provided at a location corresponding to an outer peripheral portion of the lens sheet 110. Therefore, in a case where each prism constituting the first lens group 112 or the second lens group 114 of the lens sheet 110, as illustrated in FIG. 12, is formed to have a narrow apex angle and be deep so as to improve the deflection effect, air remains in the vicinity of the apex angle of a groove of the molding cavity provided in the molding die so as to form each prism. Hence, each prism of the lens sheet 110 may not be exactly formed, resulting in degradation in the moldability of the lens sheet 110.
Also, regarding the light emission of the illumination device using the pseudo white LED 100 as the light source as described above, there is the following tendency: when the optical axis C of the pseudo white LED 100 is considered as a center, a central portion is slightly tinged with blue and an outer edge portion is slightly tinged with yellow. The reason is as follows. In FIG. 11, the outgoing light L1 follows an optical path parallel to the optical axis C of the pseudo white LED 100, while the outgoing light L2 follows an optical path inclined with respect to the optical axis C of the pseudo white LED 100. Therefore, the outgoing light L2 passes through the transparent resin 106 in which the yellow phosphors 108 are dispersed for a longer optical path length, and thus a ratio of the wavelength conversion to the fluorescent yellow light due to the yellow phosphors 108 becomes higher, as compared with the outgoing light L1.
Furthermore, in the above illumination device, the pseudo white LED 100 including the plurality of blue LEDs 102 disposed adjacent to one another is used as the light source. In this case, the light emission from the illumination device may cause color unevenness called “chip appearance” on an irradiated surface. This is a visible phenomenon caused by a series of light with high blue chromaticity and high luminance in the outgoing light from the respective blue LEDs 102 on the irradiated surface.
Such color unevenness of the illumination light causes deterioration of quality. This is not a matter in the case of the conventional illumination device using an incandescent lamp or a fluorescent lamp but peculiar to the illumination device using the pseudo white LED 100 as the light source.